The present invention relates to a high pressure/high temperature (HP/HT) process for making cubic boron nitride (CBN) ceramic masses and more particularly to a process which utilizes a single HP/HT processing operation in the manufacture of CBN ceramic masses.
The manufacture of CBN by the HP/HT process is known in the art and is typified by the process described in U.S. Pat. No. 2,947,617, a basic monocrystalline CBN case. U.S. Pat. No. 4,188,194 describes a process for making sintered polycrystalline CBN compacts which utilizes pyrolytic hexagonal boron nitride (PBN) in the absence of any catalyst. An improvement on such direct conversion process is disclosed in U.S. Pat. No. 4,289,503 wherein boric oxide is removed from the surface of the HBN powder before the conversion process.
A compact is a mass of abrasive particles bonded together in a self-bonded relationship (see U.S. Pat. Nos. 3,852,078 and 3,876,751); by means of a bonding medium (see U.S. Pat. Nos. 3,136,615, 3,233,988, 3,743,489, 3,767,371, and 3,918,931); or by means of combinations thereof. A composite compact is a compact bonded to a substrate material, such as cemented metal carbide. U.S. Pat. No. 3,918,219 teaches the catalytic conversion of hexagonal boron nitride (HBN) to CBN in contact with a carbide mass to form a composite CBN compact. Compacts or composite compacts may be used in blanks for cutting tools, drill bits, dressing tools, and wear parts (see U.S. Pat. Nos. 3,136,615 and 3,233,988).
Sintered CBN/cermet compacts prepared by HP/HT pressing of mixtures of CBN, various cermets, and aluminum compounds (with or without metal additions) are disclosed in U.S. Pat. Nos. 4,334,928 and 4,389,465. U.S. Pat. No. 4,394,170 proposes a composite sintered compact containing high density BN (CBN and Wurtzite boron nitride, WBN), ceramic and various metal bases obtained by HP/HT processing of mixtures of CBN, WBN, and various ceramic and metal mixtures. A supported version of such CBN/cermet compact is disclosed in U.S. Pat. No. 4,403,015. These prior CBN cermet compact disclosures, however, must initially make the CBN in one HP/HT step and the CBN cermet product in a second HP/HT step. Extra wear of the HP/HT presses, reduced throughput, and increased manufacturing costs result from the use of two different HP/HT processing operations.